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研究生:謝宗穎
研究生(外文):Chung Ein Hsien
論文名稱:有效的炭筆畫成像演算法之研究:以描繪樹木插畫為例證
論文名稱(外文):A Study of Efficient Rendering Algorithms for Pen-and-Ink Illustration of Trees
指導教授:王宗銘王宗銘引用關係
學位類別:碩士
校院名稱:國立中興大學
系所名稱:資訊科學研究所
學門:工程學門
學類:電資工程學類
論文種類:學術論文
論文出版年:2003
畢業學年度:91
語文別:中文
論文頁數:106
中文關鍵詞:炭筆畫樹木
外文關鍵詞:pen-and-inktreeillustration
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炭筆插畫(pen-and-ink illustration)具有簡化不必要的訊息、傳達重要的資訊、較佳的攜帶性、儲存需求比較低等優點,故以往大量使用建築學、醫學繪圖、考古學書籍內。樹木在生活週遭扮演著綠化環境、美化家園的功能,但以樹木為主體的炭筆插畫卻較少被研究與探索。本篇論文便是以炭筆插畫為研究目標,而以樹木為例證。
我們的目的是發展以樹木為成像目標有效的炭筆畫風格之成像演算法。類似於Deussen之做法,我們以三維度樹木模型作為輸入,並將樹幹與樹葉的成像分開來處理。在樹幹的成像方面,我們選擇可以保持影格間連續性之做法,採用貼圖方式產生樹幹表面之色調明暗變化。根據樹幹表面跟光線的相對關係,判斷物體處在向光面或是被光面,再透過映成的方式將原先設定好之筆觸貼圖投映在樹幹的表面。不像隨機產生筆觸方向與筆觸長短的做法,影格間連續性可以有效地控制,在執行效率方面的表現也讓人滿意。
在樹葉的成像方面,我們認為Deussen提出的深度差異演算法(depth difference algorithm)在偵測樹葉之輪廓線條時,無法精確地偵測出輪廓線條。在成像的處理上,需要經過繁瑣的參數調整。針對這兩個問題,我們分別提出濾過器演算法(filter algorithm)與標準差演算法(standard deviation algorithm)來解決。濾過器演算法是根據Soble Kernel計算像素的坡度向量,分別檢測水平方向與垂直方向的邊緣變化,再根據像素點之坡度向量的強度判斷該像素是否屬於輪廓線條。濾過器演算法所偵測出的樹葉輪廓線條比深度差異演算法偵測出的樹葉輪廓線條來的精確。標準差演算法則是以統計學的觀念,統計分析某像素群之深度值的變動程度。從像素群之深度值的分佈,計算這些像素群之深度值的平均值。像素群之深度值與平均值的差異量,便可獲得該像素群之深度值的變動值。再根據像素群之深度值的變動值,可以很容易地偵測樹葉輪廓線條。標準差演算法所偵測出的樹葉輪廓線條比深度差異演算法偵測出的樹葉輪廓線條來的精確,而且不再需要調整臨界值的設定。實作結果顯示,成像的品質優於Deussen提出之深度差異演算法所產生的結果,而且可以達到即時成像的執行效率。
  我們認為樹木炭筆畫在構圖上還需加入植披與樹影,填補插畫構圖上的空白區域,可以讓構圖上更為完整。所以,我們提出非均勻分布演算法(non-uniform distribution algorithm),可以在樹影所在之鄰近地平面作局部區域的取點。非均勻分布演算法是根據機率密度函數,隨機決定扇形內不同長度與不同角度之座標點。樹影部分,則是先將三維度樹木模型投映在地平面上,再對投映到地平面上之幾何資訊隨機取點。最後將雜草模型移動到植披與樹影的座標點上,便可以產生樹木鄰近的植披與樹影。
在即時瀏覽時,當樹木與觀察者距離太遠,則偵測樹葉輪廓線條時會判斷不出足夠的輪廓線條。Deussen提出的輪廓精準演算法可以有效地解決這個問題。但是,當樹木與觀察者距離太近時,則偵測樹葉輪廓線條時會判斷出多餘的輪廓線條。所以,我們提出了近距離輪廓精準演算法(near distance recover algorithm),以彌補Deussen所提出的輪廓精準演算法在這方面之不足。最後,我們根據上述的演算法實作了「樹木之炭筆畫風格成像系統」。使用者可以透過此系統提供之使用者介面,選取不同的成像演算法或是調整視點與其他參數,快速且有效地將任意的複雜三維度樹木模型,模擬合成為樹木炭筆畫風格之插畫。
總結本研究,我們針對樹幹的成像提出筆觸貼圖映成的做法,針對樹葉的成像提出了濾過器演算法與標準差演算法,針對即時瀏覽提出了輪廓精準演算法,最後並實作了樹木之炭筆畫風格成像系統。靜態成像方面,不再需要調整臨界值的設定,在成像處理上更為便利,所偵測到的樹葉輪廓線條也較為精準正確。並且在局部區域加入植披與樹影,讓成像構圖上更為完整。動態瀏覽方面,一秒鐘大約可以產生5張樹木炭筆插畫,並且可以維持每個影格之間的連續性。整體上,可以產生輪廓線條細緻的樹木炭筆插畫成像品質,並且具有即時成像與互動瀏覽的成像效率。筆者認為本研究對於樹木炭筆畫風格成像方面有具體貢獻。

Pen-and-Ink illustrations have the superiors of simplifying unnecessary messages, conveying important information, better carriage, and lower demands of storage, so that it had been used for architecture, medical photographing, and ancient books. Trees play a role of greening circumstances, beautifying home-land functions in our lives, however the Pen-and-Ink illustrations majoring on trees are less to be researched and discovered. This thesis makes Pen-and-Ink illustrations as the research issue, and enumerates trees for example.
Our goal is to develop an effective rendering algorithm with Pen-and-Ink illustrations style based on trees. Similar to Deussen, we use 3D tree models as input, and then render skeleton and leaves separately. In the aspect of skeleton, in order to keep the coherence among frames, we adopt texture mapping to produce the variance of shades and brightness of the skeleton surfaces. According to the relationship between the surface and the light, we can judge whether the object is on the facing-light or not, and then project the stroke textures on the surface. Unlike producing the direction and length of strokes randomly, the coherence among frames can be controlled effectively, and the efficiency is also satisfying.
In the aspect of leaves, Deussen’s depth difference algorithm can’t detect the outlines of leaves precisely. While rendering, it needs to adjust complex variables settings. Therefore, we propose filter algorithm and standard deviation algorithm to improve these disadvantages. Filter algorithm that is based on Sobel kernel calculates the gradient vectors of pixels to detect the changes of edges of horizontal and vertical directions, and judges if the pixel belongs to outlines using the magnitude of gradient vector. Filter algorithm detects more precise leaves outlines than depth difference algorithm does. The standard deviation algorithm whish is based on the statistics concept analyzes the average of the depth values of pixels. With the differences between depth value and averages of pixels, we can get the changes of the depth values of pixels and easily predict the outlines of leaves. The standard deviation algorithm detects outlines of the leaves more precise than the depth difference algorithm, and doesn’t adjust the threshold. The experimental results show that the quantity of the images using our methods is superior to Deussen’s depth difference algorithm, and it also can achieve real-time rendering.
We think if we can add graftal and the shadow of tree in the Pen-and-Ink illustrations of trees to fill up the blank area of illustrations, the composition of an image will be more accomplished. Therefore, we propose a non-uniform distribution algorithm, which can take non-uniform samples according to the distance to the tree according some kind of probability density function we developed. In the aspect of the shadow of tree, we project the vertices of 3D tree models on the ground, and then randomly choose some of the projected vertices on the ground. Finally we attach the grasses model on the location of sampling point, to produce the effects of graftal and the shadow of tree.
In real-time browsing, when the observer is far from the tree, the depth difference algorithm can’t detect the outline of leaves precisely. Deussen propose the silhouette recover algorithm can resolve this problem effectively. But when the observer is too close to the tree, the algorithm will produce exceeding outline of leaves. Therefore, we propose the near distances recover algorithm to make up the short of Deussen’s algorithm. Finally, we implement a system called “Pen-and-Ink Style of Trees Illustration Rendering System” according to above proposed algorithms. Users can easily select different rendering algorithms or adjust the viewpoint or other parameters to generate effectively an illustration of tree with Pen-and-Ink style.
In this thesis, we propose a texture mapping of strokes in the aspect of skeleton, the filter algorithm and the standard deviation algorithm for rendering leaves, the near distances recover algorithm for real-time browsing, and finally implement the “Pen-and-Ink Style of Tree Illustration Rendering System”. In the static rendering, it needn’t adjust the threshold for the convenient on rendering and the outlines are more precise and exact. Besides, attaching the graftal and tree shadow makes the composition of an image more attractive. When dynamic browsing, it could produce five images of Pen-and-Ink style of tree illustration per second, and can maintain coherence among frames. In conclusion, our rendering algorithms can produce fine-quality outlines of Pen-and-Ink style of tree illustration, and can achieve real-time rendering and interactive browsing. We think our research has a great contribution on the Pen-and-Ink style of tree illustration rendering.

第一章 緒論
1.1 研究動機 1
1.2 研究目標
1.3 論文架構
第二章 文獻回顧
2.1炭筆畫成像技術之相關文獻回顧
2.1.1 物體基準系統
2.1.2 影像基準系統
2.2樹木炭筆畫插圖成像演算法
2.2.1前置作業
2.2.2樹幹之描繪
2.2.3樹葉之描繪
2.2.4多層次抽象化
2.3研究分析與心得
第三章 炭筆畫樹木插圖成像演算法
3.1成像流程剖析
3.2樹幹的描繪技術
3.2.1輪廓線條
3.2.2色調變化
3.3樹葉的描繪技術
3.3.1深度差異演算法之重新詮釋
3.3.2濾過器演算法
3.3.3標準差演算法
3.4不同的炭筆畫風格成像方式
3.5 植披與樹影的描繪技術
3.6保持輪廓精確演算法
第四章 實作結果與分析
4.1測試模型與測試環境
4.2使用者介面說明
4.3樹木之炭筆畫風格成像系統成像結果
4.4測試數據與結果分析
第五章 結論與未來工作
5.1結論
5.2未來工作
參考文獻
詞彙索引
中英詞彙對照表
英中詞彙對照表

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